1. Field of Invention
The present invention relates to a circuit board and its fabrication process, specifically, to a circuit board with embedded passive component and the fabrication process thereof.
2. Description of Related Art
As the integration level of electronic products is getting higher and higher, the circuit layer of high integration electronic products has evolved into 6-layer, 8-layer and even 10-layer from single-layer and dual-layer circuit, so that the electronic components can be mounted on the printed circuit board. Generally speaking, the most common fabrication process of circuit board is the lamination process. The alignment precision between the circuit layers and the isolation layer must be well controlled when the lamination process is used to fabricate circuit boards. Therefore, in the fabrication process of the circuit board, usually a plurality of the alignment marks are formed on the insulating layer where the circuit layers are located, and these marks are used to align the insulating layers and one or two of the circuit layers on the surfaces of the insulating layers, and then these insulating layers and circuit layers are laminated, so that the multi-layer circuit boards or the semi-finished products are formed.
FIG. 1A and FIG. 1B illustrate cross-sectional views of the fabrication process of the conventional multi-layer printed circuit board. With reference to the FIG. 1A and FIG. 1B, the fabrication process of the conventional multi-layer printed circuit board includes the following steps: First, a substrate 10 including an insulating layer 12, two circuit layers 14 and an alignment mark 16 is provided, wherein the two circuit layers 14 are respectively located on the two surfaces of the insulating layer 12, and the alignment mark 16 is on a surface of the insulating layer 12.
Next, a first substrate 20 and a second substrate 30 are respectively located on both sides of substrate 10. The first substrate 20 and the second substrate 30 respectively have the dielectric layers 22 and 32, the circuit layers 24 and 34, and the first alignment mark 26 and the second alignment mark 36 (the top-view of the alignment mark 16, the first alignment mark 26 and the second alignment mark 36 is shown as the circled area in the figures), while the circuit layer 24 and the first alignment mark 26 are collocated on a surface of the first substrate 20, and the circuit layer 34 and the second alignment mark 36 are collocated on a surface of the second substrate 30. Next, the alignment step of aligning the substrate 10, the first substrate 20 and the second substrate 30 is completed by use of rivet and X-ray to check the alignment mark 16 of the substrate 10, the first alignment mark 26 of the first substrate 20 and the second alignment mark 36 of the second substrate 30.
With reference to the FIG. 1B, after completing the alignment step, the substrate 10, the first substrate 20 and the second base layer 30 are subjected to a heat laminating and curing process to form a multi-layer printed circuit board or a semi-finished printed circuit board. Remarkably, the alignment mark 16, the first alignment mark 26 and the second alignment mark 36 are all formed through ink printing, therefore, there is an alignment error existing respectively between the alignment mark 16 and the circuit layer 14, the first alignment mark 26 and the circuit layer 24, the second alignment mark 36 and the circuit layer 34.
When the substrate 10, the first substrate 20 and the second substrate 30 are aligned by using rivet and the alignment mark 16, the first alignment mark 26 and the second alignment mark 36 (the circle area as shown in FIG. 1B), the alignment error caused by the alignment marks described above will be continuously accumulated. If the number of the circuit layers of the circuit board increases, the accumulated errors caused by the alignment marks on the substrates with circuit layers will increase accordingly.
In addition, as the number of circuit layers increases, the electric property (e.g. RC delay effect) of the circuit board will be deteriorated gradually, therefore the passive components must be added on the circuit board to improve the electric property of the circuit board. However, the normalized passive component with specific electric property is probably not fully conformed to the special circuit design, therefore the passive component can be embedded directly inside the circuit board. Thus the passive component embedded inside the circuit board can adjust the quality of the electric property of the circuit board, based on the wiring design and the choice of materials of the circuit board.